Glutamate is the most prevalent neurotransmitter in the brain. Metabotropic glutamate receptors (mGluRs) are a family of G-protein coupled receptors that regulate neurotransmission at excitatory synapses in the brain. The diversity and heterogeneous distribution of mGluR subtypes may provide an opportunity for developing drugs to selectively target a specific CNS system and ameliorate symptoms of distinct neurological disorders. However, the role of mGluRs in excitotoxicity remains controversial. The lateral septal nucleus is a major relay nucleus in the limbic system. In lateral septal neurons, mGluR agonists elicit epileptiform burst firing and greatly elevate intracellular free calcium. Preliminary data suggest that this calcium increase results in severe excitotoxicity that is independent of ionotropic glutamate receptors. The goal of this study is to determine the molecular nature of the mGluRs in the lateral septum of rats that mediate the epileptic burst firing and excitotoxicity. In Aiml, a new generation of group selective agonists and antagonists will be tested. Intracellular recordings will be used to study the effects of these drugs on the firing pattern of lateral septal neurons. Excitotoxicity in the slices will be assessed by propidium iodide (PI) loading and fluoro-jade staining. These experiments will determine whether epileptiform burst firing and excitotoxicity are mediated by group I mGluRs alone. In Aim 2, siRNA reagents that target rat mGluRl or mGluRS will be generated and used to functionally silence the expression of mGluRl or mGluRS in organotypic cultures of the rat septum. The effect of selectively reducing mGluRl or mGluRS expression on mGluR-mediated excitotoxicity will then be assessed. By combining pharmacological and RNA-interference approaches, the molecular nature of the mGluRs that mediate the epileptic burst firing and excitotoxicity in lateral septal neurons will be elucidated. The findings will provide critical information for developing drugs that can be used to treat Parkinson's diseases, seizures, psychosis and excitotoxicity associated with stroke. [unreadable] [unreadable]